The Status Of Aquatic Resources In Nansi Lake And The Optimization Of River Crab Breeding Mode

Eriocheir sinensis H. Miln-Eswards, known as the river crab, which belongs to Crustacea, Decapoda, Raptantia, Grapsidae, Eriocheir, is the specialty of China, and it is also the main aquaculture of Lake Nansi for its abundant nutrition and delicious taste. As the biggest freshwater lake in Shandong province, Lake Nansi has a large-scale culture of Chinese mitten crabs. In addition, as the main storage hub of east route of the South-to-North Water Project, high water quality demanded, combined with the increase consumption of pollution-free mitten crabs, then, the culture of mitten crabs in Lake Nansi is facing a huge challenge, but it also creates a new opportunity for transition of its aquaculture model. In the study, a field investigation was carried out for current status of aquatic resources(mainly macrozoobenthos and aquatic plant) in Lake Nansi, and then community structure of macrozoobenthos was compared between crab culture section and non-culture section for the impact of enclosure crab culture on zoobenthos. Finally, an intercropping experiment of mandarin fish in enclosure crab culture was conducted for the new aquaculture mode of mitten crabs. 1. Status of aquatic resources in Lake NansiAccording to the actual distribution of water area and its fishing function area-dividing, the author sets up 48 research position. a total of 70 macrobenthic species were recorded, of which, there are 5 species of Oligochaeta, 20 species of Gastropoda, 11 species of Lamellibranchia, 28 species of aquatic insect and 6 species of other creatures. The diversity index and richness index of macrozoobenthos are 1.051 and 0.909, respectively; density and biomass of macrozoobenthos were 756 ind/m2 and 97.88 g/m2, respectively Meanwhile, 53 species of aquatic plant were collected in the study, which belongs to 27 families and 37 categories. Among them, Potamogeton crispus, Potamogeton lucens, Nymphoides peltatum, Trapa bispinosa, Potamogeton petinatus, Myriophyllum spicatum were the dominant species in Lake Nansi, in addition, 16 dominant populations in four seasons were recorded. 2. The impact of enclosed crab culture on macrozoobenthosIn this study, a field investigation in the crab culture section and non-culture section has been carried out in Lake Nansi, the aim of which is to analyze the influence of enclosed crab culture over macrozoobenthos and the natural restorative ability of aquatic organisms. The results show that species diversity and current standing crop of macrozoobenthos have greatly reduced in crab culture section; functional feeding groups and dominant species tend to be less diverse. But in natural area, more types of macrozoobenthos have been discovered, especially the mollusk. 11 kinds of mollusk were found in natural area, among which 7 are dominant species, however, parafossarulus striatulus were the only type to be found in the crab culture section. The standing stocks in both the crab culture section and non-culture section have increased from April to December and this fact suggests that the macrozoobenthos is capable of natural restoration. But the increase is quite negligible in crab culture area, which shows that the self-restoration ability of macrozoobenthos is hindered under the pressure of river crab predation. 3. The intercropping experiment of mandarin fish in enclosed crab culture area in Lake NansiIn order to solve the problem of extra bait and to make full use of wild fish resource, the river crab and mandarin fish have been intercropped in the same area. The result shows that the intercropping not only benefits the breeding of river crab, but also brings about high profit(when the intercropping density is 3 per unit).